Dan Powell
Ph.D. Candidate

Dan Powell

A growing body of work has highlighted the evolutionary importance of genetic exchange between divergent populations. Such exchange ultimately depends on the mating decisions of individuals within sympatric populations. Therefore, understanding the evolutionary consequences of hybridization requires us to identify the mechanisms underlying mate choice. Specifically, it is crucial to understand how natural and sexual selection act on mating traits in hybrids. Further, it is important to understand how hybridization affects other measures of fitness such as growth rate and survival to maturity. Swordtail fish, members of the genus Xiphophorus, are ideal models for such studies and can offer insight into the causes and consequences of interspecific hybridization. This is true for several reasons. First, they possess both easily identifiable male secondary sexual traits, as well as female mating preferences for these traits that can be readily characterized. More importantly however, natural hybrid zones between two closely related swordtail species, X. birchmanni and X. malinche, have been identified, and are distributed over at least seven drainages, each of which likely represents an independent hybridization event. Interestingly, despite extensive collections across all known hybrid zones, the presence of F1­ hybrids has not been detected. This suggests that hybrids observed in the field are all later generation hybrids or extensively backcrossed to the parental species, and thus have undergone many generations of selection. Since later-generation hybrids and backcrosses in the wild ultimately arise from F1 and F2 hybrids, it is important to estimate the fitness effects of hybridization in the first few generations. It is the aim of my proposed work to use controlled reciprocal laboratory crosses to elucidate the genetic architecture of male traits and female preferences in the early stages of hybridization by employing next generation sequencing techniques to inform quantitative trait loci (QTL) mapping, and to evaluate early generation hybrid fitness with respect to natural and sexual selection using the simultaneous mate choice paradigm a well as other proximal measures of fitness.